Electrodeposition of fe-cr alloy



United States Patent ELECTRODEPOSITION 0F Fe-Cr ALLOY Hajime Nitto, Wakamatsu City, Fukuoka, Japan, assignor to Yawata Iron and Steel Co., Ltd., Tokyo, Japan, a corporation of Japan No Drawing. Filed Mar. 16, 1959, Ser. No. 799,413

2 Claims. (Cl. 204-43) The present invention relates to alloy plating, and more particularly, to electrodeposition of a FeCr alloy on a basis metal in an aqueous plating bath.

Briefly, the invention comprises immersing an anode and a cathodic metal into an aqueous plating bath containing bivalent or trivalent chromium ion, bivalent iron ion, and formic acid or a salt thereof, and subjecting the cathodic metal to electrodepositing a FeCr alloy.

Heretofore the electrodeposition of chromium is carried out in the hexavalent chromium electroplating bath consisting of chromic anhydride and sulfuric acid. The electrodeposition of chromium in the trivalent chromium electrolyte bath is also known.

In either case, however, the presence of iron ion in the plating bath gives an adverse effect to the electrodeposition of chromium so that an excellent electrodeposited coating on a base metal has never been attained. Ac-

cordingly, the electrodeposition of a Fe-Cr alloy platehas heretofore never been accomplished, because hydrogen evolves at the cathode and oxygen evolves at the anode in the electrodeposition of chromium in which high current densities and high voltage are used so that the hydrogen ion concentration at the cathode decreases, which, it is believed, results in the formation and precipitation of iron hydroxide at the electrodeposited plate surface due to the excess of a hydroxyl group.

It is also believed that if trivalent iron ions are present in the electroplating bath the hydroxide thereof tends to precipitate and impart a greater adverse effect to the electrodeposited plate surface than when iron ions are present as a bivalent state due to the fact that the trivalent iron hydroxide has a less solubility-product than that of bivalent iron. From this point of view, it is preferable that the electroplating bath be of a reducing nature.

Three kinds of the electroplating bath are to be considered: of hexavalent, trivalent, and bivalent chromium, respectively. However, it is clear that the electroplating bath of less atomic value is of a reducing nature. Hence it is advantageous to employ the electroplating bath of either bivalent or trivalent chromium for the electrodeposition of a Fe-Cr alloy plate since it imparts a reducing nature thereto. In this case, however, the bivalent chromium of the bivalent chromium electroplating bath is easily oxidized by the oxygen prevalent in the electroplating tank to the trivalent chromium, therefore it is a disadvantage that the electroplating operation has to be performed in the reducing bath.

Accordingly, a buffer agent, which is sufiiciently strong to inhibit the decrease of hydrogen ion concentration at the cathode in spite of the evolution of hydrogen at the cathode, should be added to the electroplating bath.

After extensive research, I have discovered that formic acid and salts thereof are effective addition agents which impart a strong bufier function as well as a reducing "ice action to the electroplating bath. These addition agents are effective because they have both reducing and buffer actions. It is to be understood that distinct addition agents, one having a reducing action only and another having a buffer action only may be employed together in place of one addition agent having both actions.

In accordance with the invention, the electrodeposition of a Fe--Cr alloy plate on the basis metal can be accomplished by electrolyzing in the electroplating bath of either bivalent or trivalent chromium added with the addition agent of the character described and also with bivalent iron ions.

The operating conditions embodying the invention are as follows:

Anode-Magnetic iron oxide electrode Cathode-Soft steel sheet Bath composition A bright alloy plating consisting of CrzFe=50z50 is obtained on the base metal by subjecting it to electrodeposition under the above operating conditions. Cathode current efficiency is about 8% The Fe-Cr alloy electrodeposited metallic sheet produced by the process of the invention is further improved in the uniformity of the alloy plate and also in corrosion resistance by the hot diffusion treatment, which results in the production of an alloy plated metallic sheet almost equivalent to a stainless steel sheet.

I claim:

1. A method of electrodepositing a FeCr alloy plate on a metallic cathode which comprises making an article to be plated the cathode in an aqueous solution, said solution consisting essentially of 0.5 mol/l. of trivalent chromium sulfate, 4.0 mol/l. of urea, 3.0 mol/l. of ammonium sulfate, 0.05 mol/l. of ferrous sulphate, 0.1 mol/l. of formic acid, and the balance water, maintaining the temperature of the solution 25 C., maintaining pH of the solution 1.6, and passing an electric current of 30 amp/sq. decimeter therethrough between an anode and said cathode.

2. A method of electrodepositing a Fe-Cr plate on a metallic cathode which comprises making an article to be plated the cathode in an aqueous solution, said solution consisting essentially of 0.5 mol/l. of trivalent chromium sulfate, 4.0 mol/l. of urea, 3.0 mol/l. of ammonium sulfate, 0.05 mol/l. of ferrous sulphate, 0.1 mol/l. of formate, and the balance water, maintaining the temperature of the solution 25 C., maintaining pH of the solution 1.6, and passing an electric current of 30 amp/sq. decimeter therethrough between an anode and said cathode.

References Cited in the file of this patent UNITED STATES PATENTS 2,693,444 Snavely et al. Nov. 2, 1954 2,739,108 Quaely Mar. 20, 1956 2,766,196 Yoshida Oct. 9, 1956 2,822,326 Safranek Feb. 4, 1958 2,824,829 Quaely Feb. 25, 1958 

1. A METHOD OF ELECTRODEPOSITING A FE-CR ALLOY PLATE ON A METALLIC CATHODE WHICH COMPRISES MAKING AN ARTICLE TO BE PLATED THE CATHODE IN AN AQUEOUS SOLUTION, SAID SOLUTION CONSISTING ESSENTIALLY OF 0.5 MOL/1. OF TRIVALENT CHROMIUM SULFATE, 4.0 MOL/1. OF UREA, 3.0 MOL/1. OF AMMONIUM SULFATE, 4.0 MOL/1. OF FERROUS SULPHATE, 0.1 MOL/1. OF FORMIC ACID, AND THE BALANCE WATER, MAINTAINING THE TEMPERATURE OF THE SOLUTION 25*C., MAINTAINING PH OF THE SOLUTION 1.6, AND PASSING AN ELECTRIC CURRENT OF 30 AMP./SQ. DECIMETER THRETHROUGH BETWEEN AN ANODE AND SAID CATHODE. 